Vascular smooth muscle cells proliferate in response to endothelial injury. This process is fundamental to the development of the pathological lesions seen in atherosclerotic plaques, saphenous vein coronary artery bypass grafts, and stenoses that recur following transluminal angioplasty procedures. The long term goal of this proposal is to understand the role of PDGF in these proliferative lesions and to develop methods of blocking the effects of PDGF stimulation in vascular disease. In view of the probable role of PDGF-related peptides in other pathological processes, including carcinogenesis, the insight gained in these studies should have impact on several diseases. PDGF stimulates cell division by acting through specific cell surface receptors. The aims of this project are to determine the structure of the PDGF receptor, to map the functional domains of the receptor, to elucidate the molecular mechanism of PDGF action, and to develop approaches to study the role of the PDGF receptor in vivo. A large effort will be devoted to structural, immunological, and protein chemistry studies of the receptors since these are likely to provide approaches to block the action of PDGF. For this work a novel method of receptor purification using the antiphosphotyrosine antibodies will circumvent limitations that had impeded progress in studies of the PDGF receptor by more conventional methods. Other new approaches employing immunoblot methods and oncogene RNA measurements in situ will be used to study the activation of PDGF receptors in the blood vessel wall following endothelial injury in vivo. Thus for the first time, it should be possible to study the biochemistry of the mitogenic response in very small amounts of tissue. Additional biochemical studies are planned to investigate the molecular mechanism by which the PDGF receptor transmits mitogenic stimuli to the nucleus. Finally, studies of biopsy specimens will focus on whether patients with unexplained severe atherosclerosis have a hyper-responsive PDGF system. The results of these investigations should provide a better understanding of the basic aspects of PDGF action and should aid in the development of new therapeutic and prophylactic approaches to vascular disease.